Spatial cognition is essential to accomplish everyday tasks; without proper spatial functioning, people and animals wouldn’t be able to effectively navigate their environments and find food or shelter. The primary focus of my research is concerned with the neural and behavioral components of spatial learning and memory. I examine this issue by utilizing a new task I have developed, called the Sand Maze.
Considerable research has pointed to hippocampal formation and parietal cortex involvement in spatial learning and memory. O’Keefe and Nadel (1978) proposed a theory stating that the hippocampus is important for processing spatial information and forming “cognitive maps”. Hippocampal and parietal cortex involvement in spatial tasks have been shown numerous times (e.g., Kesner, Farnsworth, and DiMattia, 1989; Morris, Garrud, Rawlins, and O’Keefe, 1982; Olton and Papas, 1979). In addition, neurophysiological recording studies have shown that specific “place cells” in the hippocampus become active when a subject encounters a familiar spatial location (Otto, Eichenbaum, Wiener, and Wible, 1991).
Several tasks have been designed to examine spatial cognition in animals (e.g., radial arm maze: Olton and Papas, 1979; Morris water maze: Morris, 1981; cheese board: Kesner, Farnsworth, and Kametani, 1991). Of these, probably the most extensively used is the Morris Water Maze (Morris, 1981). The Morris Water Maze requires rats to locate a hidden platform in a pool of opaque water. Subjects quickly learn to swim to the hidden platform in order to escape from the water, and they seem to do this by using extramaze cues (e.g., pictures on the walls of the room where the maze is located).
The Morris Water Maze has been an invaluable tool in spatial learning and memory research because it provides a high source of motivation (i.e., animals are highly motivated to escape from the water on to the platform). However, one potential problem with the Morris Water Maze is its mildly aversive nature. It has been suggested that the aversive water maze may lead to increased stress responses and altered response strategies (Whishaw and Pasztor, 2000). These alterations in responding may provide a picture of spatial learning and memory that reflects an aversive motivational system as well as spatial cognition.
The new task I have designed, the Sand Maze, is an appetitive spatial task, which takes advantage of the natural foraging behaviors of rats by requiring them to locate buried cereal rewards (i.e., Froot Loops cereal) in a pool of sand. This task is virtually identical to the Morris Water Maze, except it is appetitively rather than aversively motivated.
The Sand Maze may be particularly useful because it eliminates the aversive component associated with the Morris Water Maze. Numerous studies have shown that the amygdala is involved to a great extent in learning and memory of emotional information (e.g., LeDoux, 1995; McGaugh, Cahill, and Roozendaal, 1996; McGaugh, Roozendaal, and Cahill, 2000). To the extent that an aversively motivated task involves different (or additional) neural systems, the contribution of the hippocampus may be distorted. By reducing the aversiveness of the task, it is likely that the involvement of the amygdala will also be reduced. This reduction of amygdala involvement may allow for a “purer” examination of spatial learning and memory with regard to hippocampal and parietal cortex function.
My two primary objectives when working with this task have been to systematically examine the necessary parameters for the task (i.e., What are the most effective training procedures in this task?), and to examine the neural aspects of spatial learning and memory in this task (i.e., What is going on in the brain when an animal is searching for food in the maze?).
My dissertation and much subsequent research (both at Randolph College and my previous institution, Carleton College) have revolved around the first objective. The culmination of much of this work was recently published in a chapter about the sand maze that was included in a book on learning and memory tasks (Gotthard, 2006). The parameters of this task are finally to a point where I feel that we can use the task to examine more of the neural (in addition to the behavioral) components of spatial learning and memory.
Most of my previous behavioral neuroscience research involved lesion work with rats. And while lesion work is tremendously interesting and important, it is also extremely time consuming and expensive to conduct. Because of these limitations, I have turned my attention more to the psychopharmacological side of spatial behavior, although I would willingly pick up lesion work again if feasible. There are currently a number of pharmacological manipulations that produce effects similar to brain lesions. For example, the drug we are currently using in the lab (i.e., cycloheximide) is a protein synthesis inhibitor that essentially blocks new learning when injected prior to learning trials. We are using this drug to examine the necessity for protein synthesis in the sand maze and in other appetitive learning tasks.
The Sand Maze can be used to answer a number of interesting questions about spatial and even non-spatial learning and memory. By simply exposing the FL, the task becomes a non-spatial task and an additional set of questions can be asked and answered.
Some of the questions I have studied (or am in the process of considering) using this paradigm include:
A few of the questions yet to be explored include: